The present invention relates to curable fluorescent organopolysiloxane compositions and to reactive fluorescent compounds therefor. More particularly the present invention relates to silicone coatings which comprise new reactive fluorescent organopolysiloxane compounds that are durable markers in the cured silicone coatings.
Cured silicone coatings have been used for a long time in the manufacture of peelable backings for adhesive-bearing items, such as labels and tapes. An uncured silicone coating is generally applied to a substrate, such as paper or plastic film, as a thin (e.g. 0.5 micrometer) layer of a curable liquid composition and subsequently cured to a crosslinked film by the application of heat or radiation. The thus-coated backing is thereafter brought into releasable contact with an adhesive layer from which it is to be peeled.
Since the cured release coating is typically too thin and/or too transparent to be seen with the unaided eye it is difficult to determine which side of a coated backing bears the cured release coating and how continuous that coating is. Consequently, in the use of the peelable backing, there exists the possibility of bringing an uncoated, or improperly coated, surface of the backing into non-releasable contact with an adhesive layer. A method for detecting the presence and continuity of a silicone release coating on a backing, preferably during the formation of the peelable backing, would thus be beneficial. Furthermore, it is desirable to measure the amount of coating on a substrate so as to able to control the amount being applied on-line, i.e. during the production of the peelable backing, in an economical and effective manner.
The addition of visible colorants (pigments or dyes) to a curable silicone coating has been found to be generally unsatisfactory since the high levels of colorants needed to obtain visual differentiation can adversely effect the cure of the coating and/or the adhesive release properties of the cured coating. Additionally, a colored coating is sometimes aesthetically undesirable.
In another approach to the problem of coating application and detection, Libby, U.S. Pat. No. 4,250,382, claims a method for detecting a cured silicone coating on a paper substrate comprising adding a particulate fluorescent pigment to the silicone coating before the coating is applied, scanning the resulting cured coating with ultraviolet light and detecting the fluorescence. The particulate pigments are not soluble in the silicone coating and therefore must be dispersed with vigorous mechanical agitation. Patentee notes that the use of fluorescent dyes, in contrast to fluorescent pigments, in silicone resins is not suitable because the dyes inhibit the cure of the silicone and/or fail to fluoresce sufficiently in cured silicones and/or do not adequately disperse in silicone coating compositions. However, the use of particulate fluorescent pigments is less than satisfactory since a dispersed pigment can settle out of a liquid organopolysiloxane coating composition during storage, or even during shipping or application of the composition, necessitating additional effort and/or equipment for its redispersion.
U.S. Pat. No. 4,746,751 to Oviatt et al. relates to silane dye compounds Which bear a fluorescent radical and one or more silicone polymer-reactive groups, such as vinyl or alkoxy, which are subsequently covalently bonded into a curable silicone composition during its cure. The fluorescent radical can be any fluorescent moiety selected from the group of polycyclic, homocyclic or heterocyclic aromatic compounds which demonstrate fluorescence, or the extinction of fluorescence upon a chemical event, e.g. the influence of molecular oxygen. The curable compositions are said to thus be useful as gas-permeable polymer compositions for unitary non-diffusible indicator elements in oxygen-detecting fiber optic biological probes. Fluorescent organopolysiloxane compounds which contain two or more reactive radicals are not suggested as reactive components in the compositions of Oviatt et al.
Dansyl-based silicon compounds are known from U.S. Pat. No. 4,396,528 to Abbott which discloses a fluorescent inert porous particulate material which is useful for detecting radioactive substances during thin-layer chromatography. The material is prepared by reacting a coupling agent, such as H.sub.2 NCH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 CH.sub.2 Si(OCH.sub.3).sub.3 or HSCH.sub.2 CH.sub.2 CH.sub.2 Si(OCH.sub.3).sub.3 with an aqueous slurry of silica, followed by reaction with a reactive fluorescent material, such as dansyl chloride or dansyl aziridine. However, the inert particles of Abbott do not contain reactive groups, such as silicon-bonded hydrogen atoms or alkenyl radicals.
U.S. Pat. No. 4,866,152 to Lo relates to fluorescent silanes and polysiloxanes for use as optical brighteners. These fluorescent materials are prepared by a process comprising contacting an aminofunctional silicon compound with certain optical brightening agents which are, specifically, fluorescent sulfonic acids (to form a sulfonamide linkage) or fluorescent aldehydes (to form an imino linkage) and recovering the desired fluorescent organosilicon compound. Also claimed are the fluorescent organosilicon compounds, a laundry detergent or a hair dye containing the fluorescent organosilicon compounds, a fluorescent elastomeric film derived from reacting the fluorescent organosilicon compounds with a polyfunctional acrylate, a fluorescent tack-free resinous film derived from exposing the fluorescent organosilicon compounds to moisture and a quality assurance test method for indicating the extensiveness of a silicone treatment on a substrate comprising treating the substrate with the fluorescent organosilicon compounds and examining the treated substrate under ultraviolet light. While the treatment of paper to achieve whitening is suggested Patentee makes no suggestion of fluorescent adhesive release coating compositions.